Process and composition for stabilizing and vat dyeing regenerated cellulose textiles employing formaldehyde and water-soluble dextran



United States Patent Ofiice 3,065,996 Patented Dec. 4, 1962 PROCESS AND CONWOSlTEON FOR STABILIZING AND VAT DYEING REGENERATED CELLULOSE TEXTHES EMFLOYING FORMALDEHYDE AND WATER-SOLUBLE DEXTN Malvern J. Hider, Dayton, Ohio, assignor to The Cornmonwealth Engineering ompany of Ohio, Dayton, Ohio, a corporation of Ohio No Drawing. Filed Sept. 6, 1955, Ser. No. $3 2,767 10 Claims. (Cl. 8-18) This invention relates to a method of stabilizing textile material comprising regenerated cellulose while simultaneously dyeing the textile with a vat dyestuif, and to the stabilized and dyed textiles.

As is known, in the conventional practice, dyeing and stabilization of regenerated cellulose fabric is performed in separate operations, the fabric being first dyed and then stabilized against shrinkage on repeated laundering.

The dyeing operation involves:

(l) Desizing, scouring, rinsing and drying the fabric in preparation for the dyeing;

(2) Applying the vat dyestutf to the fabric by padding;

(3) Reducing the pigment to the leuco vat;

(4) Oxidizing the leuco vat to the vat pigment;

(5) Scouring the fabric;

(6) Drying the fabric;

(7) Framing the fabric to the desired width.

Following these operations, the fabric is often treated to stabilize it against shrinkage and, generally, a synthetic resin is used as the stabilizing agent. Normally, this comprises the steps of:

(8) Applying the resin to the fabric; (9) Drying the resin-treated fabric; (10) Curing the resin to insoluble condition on the fabric; (11) Scouring the fabric; (12) Drying the fabric; and (13) Framing the fabric to desired width.

and may be readily water-soluble, difficulty water-soluble or substantially water-insoluble.

Dextran may be obtained in various ways including bacterial conversion of 1,4 linkages of dextrin to 1,6 linkages of dextran. Thus, a suitable dextran-producing bacterium, such as those of the Leuconostoc mesenteroides i or L. dextranicum types may be cultivated and the whole culture, or a filtrate therefrom containing the enzyme elaborated by the bacterium introduced into an aqueous culture medium containing sucrose and appropriate inorganic salts and nitrogenous material, the mass being held until the dextran is synthesized in maximum yield.

The dextran thus obtained normally has a high molecular weight calculated to be in the millions. It may be precipitated from the culture medium by means of a water-miscible aliphatic alcohol or ketone such as methanol, ethanol, isopropanol or acetone. The precipitate may be purified and reduced to powdered condition for use with the aldehyde.

Instead of using the high molecular weight dextran as one starting reactant, dextran of lower molecular weight may be used. The relatively low molecular weight dextran may be obtained directly by known methods in accordance with which the synthesis from sucrose is effected under controlled conditions using the enzyme and in the substantial absence of bacteria and cellular debris. As is known, this synthesis by the so-called filtered enzyme method can be conducted so that at least the major portion of the dextran obtained has a molecular weight ranging from 20,000 to 200,000 (average 60,000 to 80,000). Such dextran may be used in the present process. Or the native dextran may be partially hydrolyzed by acid or enzyme action to dextran of lower molecular weight. In general, the dextran may have a molecular Weight between 5,000 and that of the native product, determined by light scattering measurements.

The dextran and formaldehyde may be used in the process as set forth above, replacing the synthetic resin of Step 8. That is, an aqueous treating medium containing the dextran and formaldehyde may be padded onto the fabric after the dyeing has been completed. Or a shortened procedure in which the fabric is simultaneously dyed with the vat dye and stabilized may be used. This shortened procedure involves these steps:

One of the problems that has heretofore confronted the trade has been the fact that those treatments which could be said to exert a limiting effect on shrinkage of regenerated cellulose fabrics on laundering have been ineffective in preventing the pulling out which normally occurs when the fabrics are subjected to final finishing. Thus, when cellulose ethers are used alone as stabilizing agents, they have been found to provide some stability to the fabric so far as dimensional shrinkage on repeated laundering is concerned but to be ineffective to prevent pull out of the fabric during final finishing. Also, many of the treatments previously proposed for stabilizing the regenerated cellulose fabrics require the use of materials that are incompatible with dyestuffs so that use thereof in conjunction with dyes is prohibited. For instance, urea formaldehyde resin, which has been proposed as a stabilizing agent for the fabric, retards the reduction of vat pigments to the soluble leuco form which must be efiected on the fabric after the resin is cured, and therefore regenerated cellulose fabrics cannot be dyed satisfactorily with a vat dyestuff applied thereto in a treating medium comprising a urea-formaldehyde resin. Other resins of this type have the same or other disadvantages.

It has also been proposed to treat the fabric with a pre-dyed cellulose ether. That treatment does not solve the problem since the cellulose ethers do not stabilize the fabric against pull out during the final finishing which must be performed after the ether has been precipitated on the fabric. Moreover, the coloring obtained by precipitating the pre-dyed cellulose ether on the fabric involves only a mechanical fixing of the dye on the fabric surface.

More recently it has been proposed to eliminate these difficulties by treating regenerated cellulose fabrics with an aqueous medium containing the dyestufi, a water-insoluble alkali soluble cellulose ether and formaldehyde curing the aldehyde under acidic conditions and, if necessary, developing the dye on the fabric. That procedure requires the use of cellulose ethers of specified viscosity and dissolved in alkaline medium. The cellulose ether must be prepared with attention to the D8. or average ratio of ether groups to anhydroglucose units of the cellulose, and dissolved in an aqueous solution of sodium hydroxide or the like, the solution obtained being then modified by incorporation of the vat dye, the formaldehyde and special hand modifiers for the fabrics, and then adjusted to a specified pH on the acid side.

The present method is an improvement over this last mentioned prior art method in that it utilizes formaldehyde and dextran as such, and a wide selection is afforded "as to the molecular weight and other properties of the dextran used. Thus, a water-soluble or water-dispersible dextran of the desired average or substantially uniform molecular weight, such as a B512 dextran (unhydrolyzed or partially hydrolyzed to any desired extent down to an average of about 5,000) may be simply dissolved in Water, a vat dye and formaldehyde added and the pH adjusted to the value at which curing of the formaldehyde is facilitated. Another advantage of dextran for use in stabilizing the regenerated cellulose fabric is that use thereof eliminates the need for special softening or handmodifying agents. Normally, curing of formaldehyde on a regenerated cellulose textile under acidic conditions embrittles the fabric and imparts to it a harsh hand or feel. Alkaline conditions are not desirable because of the discoloration of the textile that results. In order to minimize embrittlement of the textile as far as possible prior methods, including the method using the waterinsoluble alkali soluble cellulose ethers and formaldehyde, have utilized treating media containing special softening materials for the fabric. Unexpectedly it is found that when dextran is used, and apparently because of its inherent properties, including its inherent adhesiveness, special softeners are not required and the hand or feel of the stabilized and dyed fabric is at least as pleasing and satisfactory as if the special softener had been incorporated in the treating medium.

In accordance with a preferred embodiment of the invention, therefore, textile materials of, or predominantly of, regenerated cellulose are stabilized and dyed by a method comprising impregnating or treating the textile withan aqueous treating medium having a pH on the acid side, i.e., between 1.2 and 6.5, and containing the dyestuff, water-soluble dextran and formaldehyde, dried, heated to cure the aldehyde, and if necessary treated to develop the dye on the fabric. The drying and heating to cure the formaldehyde may be performed with or without contact pressure on the fabric or the like, but are preferably performed under tension.

In the preferred embodiment, the dye component of the aqueous acidic treating medium is a vat pigment. After the fabric is heated to cure the formaldehyde (and, apparently, efiect reaction between the aldehyde and cellulose of the fabric and, possibly with the dextran) it is treated for reduction of the insoluble vat pigment to the soluble leuco vat, followed by oxidation for regenerating the dye on the fabric. The fabric is thus stabilized against dimensional shrinkage on repeated laundering and dyed to a level shade of excellent fastness to light and Washing. The fabric is also effectively stabilized against pull-out during final finishing so that there is no change in its dimensions after the formaldehyde is cured prior to the final finishing incidental to preparing the fabric for marketing.

The treating medium used in this preferred procedure is prepared by dissolving the dextran in water, adding an aqueous paste comprising the vat pigment to the solution, incorporating the formaldehyde (37% commercial formalin) diluting to the desired concentration, and ad justing the medium to pH 1.2 to 6.5 by means of an acid onacid-liberat ing salt. Preferably, the pH regulator is a strong mineral acid such as sulfuric acid which functions as a curing or condensing agent for the aldehyde when the fabric is heated to curing temperature.

In carrying out the treatment, the aqueous treating medium at pH 1.2 to 6.5 is applied to the textile, such as a regenerated cellulose fabric, while the fabric is dried under tension, as on a tenter, at a temperature of 240 F. or below, such as between 200 F. and 240 F. The dried fabric is then heated to 300 F. to 350 F. for a time interval generally inversely related to the temperature to set the formaldehyde in insoluble condition. The dextran is also insolubilized on the fabric by this heat treatment apparently as a result of reaction thereof with the formaldehyde to form a complex. The drying and curing may be performed separately or as a continuous heat treatment, for instance by blowing hot air against the fabric on the tenter, and are preferably carried out without subjecting the fabric to pressure.

After curing the aldehyde and insolubilization thereof and of the dextr-an, the vat pigment may be reduced to the soluble leuco vat by the usual methods of reducing vat pigments, as by treating the fabric with an aqueous solution of sodium hydroxide and sodium hydrosulfite in controlled amounts. The pigment can be regenerated on the fabric carrying the reduced vat by treating the fabric with an aqueous solution of a mild oxidizing agent, for example, sodium perborate.

The aqueous treating medium of pH 1.2 to 6.5 may contain, by weight based on the weight of the medium, from 0.5 to 3.0%, preferably 1.0 to 2.0% of water-soluble dextran, from 0.01% to 5% of a vat dyestuff, and from 1% to 5%, preferably about 3% of formaldehyde. The amount of sulfuric acid added to the medium to adjust the pH thereof to the desired value in the range 1.2 to 6.5 is from 0.5% to 1.5%. The sulfuric acid is normaily added in the form of an aqueous solution of appropriate concentration.

It has been proposed, in prior art methods, to include a buffer such as sodium sulfate in the acidic formaldehydecontaining treating medium to further minimize tendering of the fabric by the sulfuric acid catalyst during curing of the aldehyde. In those methods in which an aqueous sodium hydroxide solution of water-insoluble, alkalisoluble cellulose ether is used, the sodium sulfate is formed in situ in the medium by reaction between the sodium hydroxide and sulfuric acid, an excess of the latter being employed. A buffer such as sodium sulfate may be added to the present treating medium in an amount of 0.5 to 1.5%, if desired. However, the buffer is not normally required in the media containing a watersoluble dextran.

Water-soluble dextrans include those obtained using microorganisms (or their enzymes) bearing the following NRRL designations: Leuconostoc mesenteroides B- 512; L. m. B-119; L. m. 13-1146 and L. m. B-1190. These dextrans are readily soluble in water even in their native unhydrolyzed state. Or the water-soluble dextran may be obtained by partial hydrolysis of a native water-insoluble or difficultly water-soluble dextran to the watersoluble stage.

Any vat dyestuif may be used, including those of the anthracene, indigoid or sulfide types. The insoluble pigment vat is added to the aqueous dextran solution as a paste which is dispersed uniformly through the solution by vigorous stirring.

The following examples are given to illustrate specific embodiments of the invention, it being understood that these examples are not intended as limitative.

Example I One pound of B-512 native dextran is dissolved in 10 lbs. of Water. About 0.5% of the vat dye Indanthrene Blue BCSN Dbl. Paste (Pr is mixed with 3 gallons of water, and the paste thus obtained is added to the aqueous dextran solution. Then pounds of formaldehyde (as 37% commercial formalin) is added with stirring and the mass reduced with water to gallons. A 10% solution of sulfuric acid is added to adjust the pH to 1.3. Sufiicient water is then added to provide 12 gallons of treating medium. The medium is strained.

A plain weave 100% regenerated cellulose challis fabric in the greige, made of 80 warp and 60 filling yarns is desized, boiled off, and dried on a pin tenter. The final fabric has a count of 84X 64 and Weight of 4.0 ounces per yard. It is padded through the treating medium under tension, dried on a clip frame, fed to a tenter. Hot air (330 F.) is blown against the fabric on the tenter for 2.5 minutes to cure the formaldehyde and insolubilize the dextran. The fabric is then immersed for 15 minutes in a reducing bath at 140 F. and containing 15% sodium hydroxide and 0.3% sodium hydrosulfite. The fabric withdrawn from the reducing bath is then immersed for 15 minutes in an oxidizing bath at 120 F. and containing 0.12% sodium perborate. The fabric is finally scoured at 180 F., rinsed and dried in relaxed condition.

The fabric is dyed to a deep level blue shade. its dimensional stability on repeated laundering can be tested by the Standard (ICC-T-191A Cotton Wash Test, and the shrinkage thereof on repeated laundering compared with the shrinkage of an untreated fabric of the same construction. The results obtained by subjecting the fabric to five such tests (with intermediate laundering of the fabric between each test) are shown in the table below:

Example I is repeated except that the water-soluble B-512 dextran is a partial hydrolyzate having molecular weights ranging from 20,000 to 200,000, and the dye is the vat dyestuff lndanthrene Yellow 3 RD Die. Pat. (Cl. No. 1118).

Example III A regenerated cellulose fabric as in Example I is treated as in that example, except that hydrolyzed B512 dextran as in Example 11 is used, and the dye is the vat dyestulf indanthrene Brown BRA (Pr No. 118).

Example IV The procedure of Example I is followed, except that the dye contained in the treating medium is Calcosal Jade Green NP Die. Paste (Cl. No. 1101).

Various changes and modifications may be made in details in practicing the invention without departing from the spirit and scope thereof and, therefore, it is to be understood that the invention is not to be limited except as defined in the appended claims.

What is claimed is:

1. A method of stabilizing textile materials predominantly of regenerated cellulose against progressive dimensional shrinkage on repeated washings and against normal pulling out during final finishing operations performed after stabilizing treatment, and simultaneously coloring the textile, said frabric having a soft hand or feel which consists of the steps of Wetting the fibers of the regenerated cellulose textile material with a treating fluid having a pH between 1.2 and 6.5 and consisting essentially of water, from 0.5% to 3.0% of water-soluble dextran, from 0.01% to 5% of a dispersed vat pigment and from 1% to 5% of formaldehyde, drying the textile, heating the textile to the curing temperature for the formaldehyde, treating the textile, after curing of the aldehyde, with an aqueous alkaline solution of a reducing agent to reduce the vat pigment to the soluble leuco vat on the textile, thereafter treating the textile with an aqueous solution of a mild oxidizing agent to regenerate the pigment on the textile, and then scouring, rinsing and drying the fabric.

2. The method according to claim 1, in which the fibers of the textile material are wetted with treating fluid while the textile material is under tension.

3. The method according to claim 1, in which the formaldehyde is cured and the dextran insolubilized by blowing hot air against the textile material.

4. The method according to claim 1, in which the textile material is dried under tension.

5. The method according to claim 1, in which the treating fiuid contains native, Water-soluble dextran.

6. A treating fluid for stabilizing textile materials predominantly of regenerated cellulose and simultaneously applying color to the textile material, said fluid having a pH of 1.2 to 6.5 and consisting essentially of water, from 0.5 to 3.0% of water-soluble dextran, from 0.01% to 5.0% of a dispersed vat pigment and from 1% to 5% of formaldehyde.

7. A treating fluid for stabilizing textile materials predominantly of regenerated cellulose and simultaneously applying color to the textile material, said fluid having a pH of 1.2 to 6.5 and consisting essentially of water, from 0.5% to 3.0% of native, unhydrolyzed, watersoluble dextran, from 0.01% to 5% of a dispersed vat pigment and from 1% to 5% of formaldehyde.

8. Textile material predominantly of regenerated cellulose and resulting from the method of claim 1.

9. Textile material predominantly of regenerated cellulose and resulting from the method of claim 5.

10. A woven fabric predominantly of regenerated cellulose and resulting from the method of claim 1.

References in the file of this patent UNITED STATES *PATENTS 2,238,839 Watkins Apr. 15, 1941 2,411,818 Weiss Nov. 26, 1946 2,441,859 Weisberg May 18, 1948 2,628,151 Walmsley Feb. 10, 1953 2,674,584 Deniston Apri. 6, 1954 2,706,690 Deniston Apr. 19, 1955 2,746,880 Deniston May 22, 1956 OTHER REFERENCES Owen: Sugar, August 1948, pp. 28 and 29.

Hehre: Proc. Soc. Exp. Biol. and Med., July 1949, pp. 336-339.

Owen: Sugar, May 1955, pp. 47, 48, and 64. 

1. A METHOD OF STABILIZING TEXTILE MATERIALS PREDOMINANTLY OF REGENERATED CELLULOSE AGAINST PROGRESSIVE DIMENSIONAL SHRINKAGE ON REPEATED WASHINGS AND AGAINST NORMAL PULLING OUR DURING FINAL FINISHING OPERATIONS PERFORMED AFTER STABILIZING TREATMENT, AND SIMULTANEOUSLY COLORING THE TEXTILE, SAID FRABRIC HAVING A SOFT "HAND" OR "FEEL" WHICH CONSISTS OF THE STEPS OF WETTING THE FIBERS OF THE REGENERATED CELLULOSE TEXTILE MATERIAL WITH A TREATING FLUID HAVING A PH BETWEEN 1.2 AND 6.5 AND CONSISTING ESSENTIALLY OF WATER, FROM 0.5% TO 3.0% OF WATER-SOLUBLE DEXTRAN, FROM 0.01% TO 5% OF A DISPERSED VAT PIGMENT AND FORM 1% TO 5% OF FORMALDEHYDE, DRYING THE TEXTILE, HEATING THE TEXTILE TO THE CURING TEMPERATURE FOR THE FORMALDEHYDE, TREATING THE TEXTILE, AFTER CURING OF THE ALDEHYDE, WITH AN AQUEOUS ALKALINE SOLUTION OF A REDUCING AGENT TO REDUCE THE VAT PIGMENT TO THE SOLUBLE LEUCO VAT ON THE TEXTILE, THEREAFTER TREATING THE TEXTILE WITH AN AQUEOUS SOLUTION OF A MILD OXIDIZING AGENT TO REGENERATE THE PIGMENT ON THE TEXTILE, AND THEN SCOURING, RINSING AND DRYING THE FABRIC. 